London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

Millions of families were today hit by the biggest energy prices rises yet seen this Autumn.

Npower said it was following rival British Gas and Scottish & Southern Energy with an average 9.4 per cent dual fuel hike for 3 million customers. The average increase on single fuel tariffs is 8.8 per cent for gas and 9.1 per cent for electricity.

The increase will add £108 a year to bills paid by direct debit when it comes into force on 29 November. Around 500,000 vulnerable customers will not be affected.

The announcement came hours after British Gas said it would put its tariffs up by 6 per cent. Scottish & Southern, which trades as Scottish Electric in London, is pushing through a nine per cent rise on Monday.

Paul Massara, Npower’s chief commercial officer, said: “There is never a good time to increase energy bills, particularly when so many people are working hard to make ends meet.

“But the costs of new statutory schemes, increases in distribution charges and the price of gas for the coming winter are all being driven up by external factors, for example government policy.

“Although we have managed to smooth out the worst fluctuations and protect our customers for as long as we can, we are now having to pass on some of these costs.”

Ann Robinson, Director of Consumer Policy at comparison website uSwitch.com, said: “With SSE’s hike coming into effect on Monday and both British Gas and npower announcing today, consumers are heading into a winter of discontent.

“The upshot of this triple whammy is that we can expect to be paying a record amount for our energy - the average household energy bill has never been so high and consumers will be demanding to know why.

“This is a frightening prospect – last winter over eight in ten households were rationing their energy over fear of the cost. And now the pressure of an extra £100 or so on energy bills will leave many more buckling. As we head into another winter, the potential impact on health and well-being is immense.

Npower said the spiralling cost of Government imposed environmental and social schemes, the higher cost of transporting gas and electricity and increased wholesale prices were to blame.

Npower said its half year profits had fallen 15 per cent and its parent company, the German utility giant RWE, had invested £3.4 billion “helping to keep the lights on.”